New product and process



United States fPatent C) 3,342,330 NEW PRODUCT AND PROCESS Harry W.Buchanan, Milford, Pa, assiguor to M & T Chemicals Inc., New York, N.Y.,a corporation of Delaware No Drawing. Filed May 5, 1964, Ser. No.365,174 Claims. (Cl. 206-84) This invention relates to a method ofpreparing novel collapsible tubular metal containers.

As is well known to those skilled in the art, collapsible tubular metalcontainers such as aluminum metal containers may be used in connectionwith a wide variety of products. These containers have been found tohave widespread use in the packaging of chemically inert materials, suchas tooth paste, shaving cream, hand lotion, etc. It has been observedhowever, that certain compositions may be sufiiciently reactive to adegree which prevents packaging in aluminum tubes. For example, althoughmany tooth pastes have heretofore been packaged in aluminum metal tubes,it has been found that those tooth pastes containing certain activeingredients such as stannous tin or fluorides, including stannousfluoride, may be sufliciently reactive to corrode the container.

For example, a typical aluminum tooth paste tube containing nocorrosively active materials may have an indefinitely long shelf lifeunder normal shelf conditions. In order to estimate shelf life undernormal conditions an accelerated storage test may be employed. Underaccelerated shelf life tests at 43 C., such a tube may be free ofperforation for at least several months. By comparison, an aluminum tubecontaining tooth paste, identical to the standard but additionallycontaining 1.52% stannous fluoride would last only about three days atwhich time it may be preforated.

As a result, it has heretofore been the practice to marketfluoride-containing tooth paste in lead tooth paste tubes. This isundesirable because the lead tubes cost more to fabricate and contain anuneconomically large amount of leadthis results inter alia from therequired increased wall thickness of lead. Furthermore the use of leadmetal raises the possibility of problems arising because of the wellknown toxicity of lead. This factor requires e.g. the use of a plasticspout because the action of the air with the contents in the presence oflead may discolor the tooth paste.

It is an object of this invention to prepare a novel collapsible tubularaluminum container. Other objects will be apparent to those skilled inthe art on inspection of the following description.

In accordance with certain of its aspects the method of this inventionfor preparing a collapsible tubular aluminum container comprises formingan aluminum container from an aluminum blank; cleaning said aluminumcontainer; and contacting at least the interior surface of said cleanedaluminum container with an aqueous alkaline bath containing a stannatesalt selected from the group consisting of sodium stannate and potassiumstannate; maintaining said aluminum container in contact with said bathfor time sufiicient to deposit a surface layer of tin thereon; andseparating from said bath said aluminum container bearing said surfacelayer of tin.

In accordance with certain of its other aspects, the novel compositionof this invention comprises a collapsible tubular aluminum containerhaving a surface layer of tin on the interior surface thereof.

Preparation of the aluminum con-tainer of this invention may include theextrusion of a slug or coin of aluminum metal, which may besubstantially pure aluminum, in an impact extrusion press. Duringextrusion, the slug on impacting may follow the die to form an openendedaluminum metal tube.

The so-formed metal tube may then be trimmed to uniform length, andcleaned as by immersion in a cleaning solution. Typically such acleaning solution may be an aqueous solution containing 15 g./l.60g./l., say 30 g./l. of sodium carbonate and 15 g./l.60 g./l., say 30g./l. of trisodium phosphate. During this cleaning, the aluminum tubemay be degreased and mildly etched. The tube may then be rinsed andimmersed in l0%-50%, say 25% nitric acid thereby neutralizing the alkaliand removing any smut which may be present on the surface of thealuminum.

The so-treated aluminum tube may then be further treated by contactingat least the inner surface thereof with an aqueous alkaline bathcontaining a Iongkindchelating agent, and a stannate salt selected fromthe group consisting of sodium stannate and potassium stannate,maintaining said aluminum in said bath for time suflicient to deposit asurface layer of tin thereon; and withdrawing said aluminum from saidbath.

Preferably the aluminum tube may be treated by contacting said aluminumin an aqueous bath consisting essentially of water, and a stannate saltselected from the group consisting of sodium stannate and potassiumstannate; maintaining said aluminum in said bath for time sufiicient todeposit a surface layer of tin thereon; and withdrawing said aluminumfrom said bath.

The immersion baths which may be used in practice of this invention maybe typicallymade up by dissolving potassium stannate and/or sodiumstannate in water to form a bath containing from about 15 g./l. (gramsper liter) to saturation, typically about 70 g./l. of the stannate salt,the resulting solution containing about 30 g./l. of tin. Sufficientpotassium hydroxide and/or sodium hydroxide may be initially added toform a bath containing about 4 g./l. of the metal hydroxide to preventprecipitation of tin due to low pH during make up. During operation, thefree alkali metal hydroxide may be maintained between about 0.5 g./l.and about 12 g./l., preferably between 1 g.l. and 8 g./l., say 4 g./l.Proper operation of the bath may normally be carried out at a pHsufliciently high to keep the stannate in solution. Since tin mayprecipitate from these baths at pH below about 11.5, normal operation ofthese baths may be at pH above this point and preferably at pH of atleast 12. This pH may normally be maintained automatically by thehydroxide generated and it may not normally be necessary to addhydroxide to the baths. The required free hydroxide concentration may beinitially attained by addition of potassium hydroxide or sodiumhydroxide. During operation the bath may generate sufiicient hydroxideto maintain the desired concentration.

The Jongkind-chelating agent which may be used in practice of thisinvention may be a chelating agent which is characterized by the abilityto complex or chelate at at least one metal selected from the groupconsisting of: copper in solutions containing at least 1.2 Normalhydroxide ion, and magnesium in solutions containing at least 0.7 Normalhydroxide ion, the chelating ability being present when the agent ispresent in amount of one and one-half moles per mole of copper ormagnesium metal present.

In a preferred embodiment, the Jongkind-chelating agent may typically bean anion of an aminocarboxylic acid such as ethylene diamine tetraaceticacid; water soluble salts of this compound, typically alkali metal saltssuch as the disodium salt of ethylene diamine tetraacetate; themonosodium salt of N,N-dihydroxyethyl glycine, the trisodium salt ofN-hydroxyethyl ethylene diamine triacetic acid, etc.

In accordance with certain other preferred aspects of this invention,the Jongkind-chelatingagent added to the solution may be in the form ofan anion of a polyhydroxy carboxylic acid. In a highly preferredembodiment, this anion may be an anion having less than about 8 carbonatoms. The preferred anion maybe an anion of a polyhydroxymonocarboxylic acid, typified by the gluconate ion, the glucoheptonateion, the glycerate ion, or of a polyhydroxy polycarboxylic acid typifiedby the saccharate ion or the tartrate ion. The preferred anions whichmay be employed may be gluconate, glucoheptonate, glycerate, andsaccharate.

The anions may be added as sodium or potassium salts e.g. sodiumgluconate, potassium gluconate, sodium saccharate, potassium saccharate,sodium glucoheptonate, potassium glucoheptonate, sodium glycerate,potassium glycerate, sodium tartrate, and potassium tartrate. The anionmay alternatively be added as acid, typically gluconic acid, saccharicacid, etc. or as lactone, typically glucono-delta-lactone, thedelta-lactone of glucoheptonic acid, etc.; etc. Mixtures of thesecompounds maybe employed. The Jongkind-chelating agent may be added,preferably with agitation, to the aqueous stannate bath independently orjointly with the stannates which are used to make up and also tomaintain the baths. Presence of the Jongkindchelating agent is desirableto improve the characteristics of the tin deposit, reduce sludging, andmaintain stable pH.

Preferably, the Jongkind-chelating agent may be employed as the salt inamounts of 0.01 mole to 0.25 mole, say 0.1 mole/ 1. When the agent isthe anion of the polyhydroxy carboxylic acid, equivalent amounts of acidor lactone may be employed. Smaller amounts may be employed, but they donot substantially control the thickness of the immersion plate or theformation of the sludge. Greater amounts may be employed but nosubstantial additional improvement may be obtained thereby.

In accordance with the process of this invention, the surface of thecollapsible aluminum container may be contacted with an aqueous bathcontaining stannate. Contacting may be by immersion of the tube in thebath, by spraying or brushing the bath onto the surface of thecontainer, etc. For the sake of convenience, reference will hereinafterbe made to contact by immersion. Immersion plating in accordance withthis invention may be carried out between room temperature of e.g. 20 C.and 90 C., and preferably between 40 C. and 80 C., say 60 C. Immersiontime may be as little as 30 seconds, but it is usually between 1-6minutes, say 4 minutes. During this time, aluminum may be coated with alayer of tin of desired thickness.

For make up and maintenance of the baths, preferred compositions maycontain 80%99% by weight of potassiurn stannate and/ or sodium stannateand 1%20% of at least one compound containing the Jongkind-chelatingagent, typically an anion of a polyhydroxy carboxylic acid. Preferredcompositions of matter may contain 90%-98% of the stannate and 10%2.% ofat least one Jongkind-chelating agent, e.g. a compound containing ananion of a polyhydroxy carboxylic acid. The compositions containinglower percentage of the agent e.g. 2%- 5% may be preferred forreplenishment or maintenance while the compositions with the higheragent content e.g. 5%20% may be preferred for the make up of new baths.Illustrative of these are the following compositions:

tetrasodiurn salt of ethylene diamine tetraacetic acid 1 4. sodiumstannate 86 tetrasodium salt of ethylene diamine tetraacetic acid 14 45. potassium stannate 98 monosodium salt of N,N-dihydroxyethyl glycine 26. sodium stannate 97 monosodium salt of N,N-dihydroxyethyl glycine 3 7.potassium stannate 95 potassium gluconate 5 8. sodium stannate 96 sodiumgluconate 4 9. potassium stannate 98 sodium gluconate 2 10. sodiumstannate sodium gluconate 15 11. potassium stannate 97 potassiumglucoheptonate 3 12. sodium stannate 96 sodium glucoheptonate 4 13.potassium stannate 97 sodium gluconate 3 The novel tubular aluminumcontainers which have been coated with tin by contact with the bath maybe found to have a coating of 0.5-1.5, say 1 micron on the innersurface, if the contacting has been by spraying, and on both the innerand outer surface if the contact has been by immersion. These tubes areparticularly characterized by their resistance to the corrosive effectof active compositions such as fluorides including stannous fluoride intooth paste. As a further advantage, the tin coating on the interior ofthe tooth paste tube may serve as a means for reducing stannic tin ionto stannous tin. This is desirable because tin in the stannic formpossesses little or no activity as an anti-caries agent.

The novel collapsible tubes of this invention may comprise a collapsibletubular aluminum container having a surface layer of tin on the interiorsurface thereof. These novel containers are highly useful containers forany substance which is corrosive in nature and which is therefore notcapable of being stored for prolonged periods.

The containers of this invention are particularly useful in combinationwith tooth pastes containing stannous tin or fluoride as an activeingredient. A preferred combination is a novel collapsible tubularaluminum container having a surface layer of tin on the interior surfacethereof; and, within said container, tooth paste containing at least oneactive ingredient selected from the group consisting of stannous tin andfluoride. In accordance with certain preferred aspects of thisinvention, the active ingredient in said novel combination may bestannous fluoride.

In one series of comparative illustrative examples, pairs of tooth pastetubes which had been impact extruded from 99.7+% aluminum metal weretested. One series of tubes was tin plated on the inside and the outsideby immersion plating in a bath containing 60 g./1. of potassium stannateK Sn(OI-I) 11.25 g./l. of sodium gluconate, and 3.75 g./l. of potassiumhydroxide. The tubes were immersed for one minute at 48 C. to form acoating of tin having a thickness of one micron on the inside and theoutside of the tubes. The tubes were filled with a typical tooth pasteformulation which may be made up as follows:

Component: Parts by weight CaHPO -2H O 41.6 Synthetic detergent (Nalauryl sulfate) 1.4 Glycerine 25.0 Water 28.0 Irish moss extract 1.5Stannous fluoride 1.6

Flavoring 0.9

Total 100.0

The Irish moss extract was wet out in part of the glycerine and thecalcium phosphate (dibasic) was wet out in part of the water, in whichthe synthetic detergent had been dissolved. These slurries were thenmixed together with heating until a uniform temperature of 70 C. wasreached. The thickened paste mixture was then cooled to a temperature of35 C. and the flavoring, the remaining glycerine and the remaining watercontaining the stannous fluoride were all added and mixed in thoroughlyto give a homogeneous paste of suitable consistency.

Aluminum tubes were filled with equal amounts of the above composition.The tubes, both untreated and treated, were stored at 43 C. The tubeswere inspected daily. It was apparent from inspection that the tubes hadbecome perforated after a certain time because of the appearance ofwhite spots on a substantial portion of the surface.

It was apparent after only three days of this accelerated testing thatthe aluminum tubes which had not been treated by practice of thisinvention were substantially entirely perforated. The tubes which hadbeen treated as indicated by application thereto of a tin coating werefound to be substantially free of perforation up to about thetwenty-third day under the very severe conditions of the acceleratedtest.

Thus it is apparent that the practice of this invention permitsattainment of tubes which have a shelf life under accelerated storage(which correlates readily with normal storage conditions) which may beeight times as long as the standard aluminum tube normally employed.

Although this invention has been illustrated by reference to specificexamples, numerous changes and modifications thereof which clearly fallwithin the scope of the invention will be apparent to those skilled inthe art.

I claim:

1. A novel collapsible tubular aluminum container having a surface layerof tin on the interior surface thereof.

2. A novel container as claimed in claim 1 wherein said layer of tin hasa thickness of 0.5-1.5 microns.

3. A novel collapsible tubular aluminum container having a surface layerof tin on the interior surface thereof; and, within said container,tooth paste containing at least one active ingredient selected from thegroup consisting of stannous tin and fluoride.

4. A novel container as claimed in claim 3 wherein said layer of tin hasa thickness of 0.5-1.5 microns.

5. A novel collapsible tubular aluminum container having a 0.5-1.5micron surface layer of tin on the interior surface thereof; and, withinsaid container, tooth paste containing stannous fluoride.

References Cited UNITED STATES PATENTS THERON E. CONDON, PrimaryExaminer.

I. M. CASKIE, Assistant Examiner.

5. A NOVEL COLLAPSIBLE TUBULAR ALUMINUM CONTAINER HAVING A 0.5-1.5MICRON SURFACE LAYER OF TIN ON THE INTERIOR SURFACE THEREOF; AND, WITHINSAID CONTAINER, TOOTH PASTE CONTAINING STANNOUS FLUORIDE.